Revisiting Self‐Assembled Photo‐Responsive Hydrogels: Molecular Design Strategies and Biomedical Applications

Self‐assembled photo‐responsive hydrogels, often termed as smart materials , have gained great acceptance mainly due to their importance in biomedical research. A photo‐responsive unit is decorated with a supramolecular function and hydrophilic/hydrophobic chains (discreet or polymeric) during the molecular design toward the fabrication of such smart materials. Different photo‐responsive cores, such as azobenzene, spiropyran, stilbene, etc., have been explored for these purposes. Notably, various noncovalent interactions have been exploited to make hydrogels via molecular self‐assembly approach. Insertion of the H‐bonding unit is the most common method adopted by many groups; however, other supramolecular interactions, like hydrophobic, π−π stacking interactions have also been used to create smart materials. Most of these materials have been employed mainly in biomedical applications, as these aqua materials are biocompatible and responsive toward many biological stimuli in living materials. Most common biomedical application targets are site‐specific drug delivery, cancer therapy, wound healing, etc. This review focuses on the progress of the various molecular design strategies adopted to fabricate self‐assembled hydrogels that respond to light and their biomedical applications. We envisage that a revisit to this topic is important based on the recent advancement of responsive hydrogels toward adaptive and intelligent soft matter.